Page 66 - ACCB 2020

Revista de la Asociación Colombiana de Ciencias Biológicas
issn impreso 0120-4173, issn en línea 2500-7459
MECHANISMS OF ARBUSCULAR MYCO- uptake of large amounts of nutrients, including heavy
RRHIZAL FUNGI IN PROMOTING PLANT metals (43-44). Some of these fungi have also evolved
GROWTH AND PRODUCTIVITY a heavy metals tolerance (45-46).
Mechanism for the biocontrol of pathogens
The soil-borne pathogens usually controlled by agri- Mechanism for enhanced Nutrient Uptake
cultural practices such as chemical, fungicides, soil fu- AM fungi facilitate the uptake of primary soil nutrients
migation, resistant cultivars, crop rotation, etc., are not (N, P, K) as well as Mg, Ca, Cu, Zn, Fe, Ni, Cd through
effective in the long-term due to various reasons. Conse- plant roots. The hyphal network is optimally stationed to
quently, researchers tried to use alternative approaches effi ciently absorb nutrients and water from the soil but
based on manipulation and addition of microbes to in- only a few of these transporters are involved, especially
fl ate the plant protection against pathogens (34). The those who are responsible for the uptake of phosphate,
biocontrol of pathogens was facilitated by utilization of ammonium, and zinc. Since diffusion is quite slow, the
benefi cial microorganisms (Pseudomonas fl uorescens) nutrients are made to move in a packaged form amongst
and fungi (AMF and Trichoderma) that compete for extra-radicle and intra-radicle mycelium. Some AMF
nutrient uptake and space with plant pathogens, they synthesize phosphatases which enhance mineralization
parasitize the pathogen and produce antibiotics thus of organic phosphate and increase phosphate availabi-
impelling resistance in the host plant (35). AM fungi lity, whilst few AMF produces organic acids which op-
symbiosis compensates for the loss of root biomass or timizes the pH and in turn increases its emulsifi cation
function caused by pathogens thus boosting the toleran- and availability of phosphate (47-48). Under conditions
ce level of the host to attack by pathogen (36), nema- of reduced phosphorus availability, the AMF interfered
todes (37) and fungi (38). A reduction in the soil-borne transfer of nutrients has been observed from the host
pathogenic diseases, caused by fungal pathogens such plant to another plant through AM hyphal colonies. For
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as Phytophthora, Gaeumannomyces, Fusarium, Chala- example, C photosynthate from one plant to another
ra (Thielaviopsis), Pythium, etc was observed when AM was transported primarily through AM hyphae instead
fungi interacted with plant pathogenic fungi (38). Some of leaking out through roots of the donor plant. While in
of the mechanisms that can explain bio-control by AMF 32 P experiment, the hyphal linkage between plants was
include biochemical changes in plant exudates, e.g. pe- the dominant factor for the transfer (49).
roxidases, phytoalexins, phenolics, etc., changes in the
rhizosphere microbial fl ora, change in nutrient status of Further Nutrient uptake is easier under mycorrhizal
the host, anatomical changes in root cells, changes in inoculation; even in saline conditions (50-52). N uptake
the root system morphology of the host plant that faci- was increased in the presence of Glomus sp. in saline
litates damage compensation, tolerance to heavy metals conditions by Cajanus cajan and Sesbania sp. respec-
and stress alleviation (39). tively (53-54). AMF symbiosis increased biomass ac-
cumulation and photosynthate production by increasing
Mechanism of phytoremediation the mobilization of various macro-nutrients (N, P, K,
The effect of AMF on metal uptakes is infl uenced by va- Ca, S) and micro-nutrients (Fe, Cu, Zn) into plants (55).
rious factors, such as fungal genotype, the type and con- Under different irrigation regimes it has been observed
centration of metal, interaction between P and the metal that, AMF symbiosis promote development in plant at
to name a few (40). Studies have suggested that AMF higher and lower P levels by maintaining N and P up-
R. Pseudoacacia, due to its fast growth, high biomass, take (56).
its capacity of accumulating large amounts of heavy
metal (HM), and atmospheric nitrogen fi xation, have Alteration of root structure and space
the potential for extracting metal contaminants from AM colonization changes the root architecture of the
soil (41). Higher root to shoot Pb ratio in mycorrhizal host plant (57). The plants show an increase in root
plants enhances Pb uptake and accumulation in the root growth and branching, (21) meristematic, nuclear ac-
system. R. intraradices plays a sequestering role in Pb tivity of the root cells and root morphology. This may
detoxifi cation (42). Fungal vacuoles play an important increase the nutrient uptake and change the rhizosphere
role in retention, binding, and immobilization of heavy interaction exceptionally in pathogen-infection develo-
metals. They facilitate the regulation of cytosolic me- pment (58). The root morphology emerging from AM
tal ion concentrations and detoxifi cation of toxic metal colonization seems to be contingent with the specifi city
ions. The long extramatrical fungal hyphae help in the of the plant. It mostly appears to be more accounting

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Rev. Asoc. Col. Cienc.(Col.), 2020; 32: 63-76